A flat panel display may comprise a matrix of optical shutters commonly referred to as pixels or picture elements as illustrated in FIG. 1. FIG. 1 illustrates a flat panel display 100 comprised of a light guidance substrate 101 which may further comprise a flat panel matrix of pixels 102. It is noted that flat panel display 100 may comprise other elements than illustrated such as a light source, an opaque throat, an opaque backing layer, a reflector, and tubular lamps, as disclosed in U.S. Pat. No. 5,319,491, which is hereby incorporated herein by reference in its entirety.
Each pixel 102, as illustrated in FIGS. 2A and 2B, may comprise a light guidance substrate 201, a ground plane 202, a deformable elastomer layer 203, and a transparent electrode 204.
Pixel 102 may further comprise a transparent element shown for convenience of description as disk 205 (but not limited to a disk shape), disposed on the top surface of electrode 204, and formed of high-refractive index material, preferably the same material as comprises light guidance substrate 201.
In this particular embodiment, it is necessary that the distance between light guidance substrate 201 and disk 205 be controlled very accurately. In particular, it has been found that in the quiescent state, the distance between light guidance substrate 201 and disk 205 should be approximately 1.5 times the wavelength of the guided light, but in any event this distance must be maintained greater than one wavelength. Thus the relative thicknesses of ground plane 202, deformable elastomer layer 203, and electrode 204 are adjusted accordingly. In the active state, disk 205 must be pulled by capacitative action, as discussed below, to a distance of less than one wavelength from the top surface of light guidance substrate 201.
In operation, pixel 102 exploits an evanescent coupling effect, whereby TIR (Total Internal Reflection) is violated at pixel 102 by modifying the geometry of deformable elastomer layer 203 such that, under the capacitative attraction effect, a concavity 206 results (which can be seen in FIG. 2B). This resulting concavity 206 brings disk 205 within the limit of the light guidance substrate's evanescent field (generally extending outward from the light guidance substrate 201 up to one wavelength in distance). The electromagnetic wave nature of light causes the light to “jump” the intervening low-refractive-index cladding, i.e., deformable elastomer layer 203, across to the coupling disk 205 attached to the electrostatically-actuated dynamic concavity 206, thus defeating the guidance condition and TIR. Light ray 207 (shown in FIG. 2A) indicates the quiescent, light guiding state. Light ray 208 (shown in FIG. 2B) indicates the active state wherein light is coupled out of light guidance substrate 201.
The distance between electrode 204 and ground plane 202 may be extremely small, e.g., 1 micrometer, and occupied by deformable layer 203 such as a thin deposition of room temperature vulcanizing silicone. While the voltage is small, the electric field between the parallel plates of the capacitor (in effect, electrode 204 and ground plane 202 form a parallel plate capacitor) is high enough to impose a deforming force on the vulcanizing silicone thereby deforming elastomer layer 203 as illustrated in FIG. 2B. By compressing the vulcanizing silicone to an appropriate fraction, light that is guided within guided substrate 201 will strike the deformation at an angle of incidence greater than the critical angle for the refractive indices present and will couple light out of the substrate 201 through electrode 204 and disk 205.
The electric field between the parallel plates of the capacitor may be controlled by the charging and discharging of the capacitor which effectively causes the attraction between electrode 204 and ground plane 202. By charging the capacitor, the strength of the electrostatic forces between the plates increases thereby deforming elastomer layer 203 to couple light out of the substrate 201 through electrode 204 and disk 205 as illustrated in FIG. 2B. By discharging the capacitor, elastomer layer 203 returns to its original geometric shape thereby ceasing the coupling of light out of light guidance substrate 201 as illustrated in FIG. 2A.
However, the electrostatic actuators that involve parallel plate capacitor interaction, such as those disclosed in U.S. Pat. No. 5,319,491, often involve a large array of variable gap capacitors. Over large areas, registration (the term given to the optical alignment and geometric coincidence of complementary device components topologically disposed on either consecutive or nonconsecutive parallel planes in spaced-apart relation) between the discrete top and bottom capacitor plates becomes progressively more difficult to achieve, until the registration error is multiplied to the point that a large number of top and bottom plates no longer adequately register. That is, the top and bottom plates fail to coincide geometrically due to differential dimensional drift incurred during fabrication and/or assembly of the respective laminae on which the discrete elements are disposed. Therefore, there is a need in the art to implement a registration-free, contiguous conductive plane that is itself flexible and capable of plate bending motion either alone or in tandem with an associated elastomeric layer.
The images displayed on a display, such as the one disclosed in U.S. Pat. No. 5,319,491, do not correspond to physical reality for a number of reasons, apart from the two-dimensional flattening of three-dimensional real world entities. One of the reasons for a displayed image to not correspond to physical reality involves chrominance. Chrominance is the difference between a color and a chosen reference color of the same luminous intensity. The chrominance range, i.e., the range of difference between a color and a chosen reference color of the same luminous intensity, has been limited in order to keep display costs down. Consequently, the gamut of color reproduced on the display is limited. Typically, displays, such as the display disclosed in U.S. Pat. No. 5,319,491, use the three standard tristimulus colors, e.g., red, green and blue (RGB). That is, these displays modulate only three primary colors across a screen surface. By increasing the colors modulated across the screen surface, i.e., by extending the color gamut displayed, the image displayed will more closely correspond to physical reality. Therefore, there is a need in the art to extend the colors beyond the ability of RGB systems to reproduce without extensible modifications to such displays.
Furthermore, infrared and other non-visible light displays are generally not integrated into an existing full color RGB display. There is a need in the art for consolidating RGB and infrared (or other non-visible light(s)) in several disciplines, most notably avionics, where cockpit real estate is at a premium.
Furthermore, the display, such as the one disclosed in U.S. Pat. No. 5,319,491, incorporates FTIR (Frustrated Total Internal Reflection) means to emit light from the display surface. If an evanescent wave (such as that produced by total internal reflection), which extends approximately one wavelength beyond the surface of a separating medium of lower refractive index, should be invasively penetrated by a region occupied by a higher index of refraction material, energy may flow across the boundary. This phenomenon is known as evanescent coupling. Evanescent coupling is an effective means to achieve frustrated total internal reflection and bears affinity to quantum mechanical tunneling or barrier penetration.
Flat panel displays, such as the one disclosed in U.S. Pat. No. 5,319,491, that incorporate FTIR means are not curved. Consequently, the distance between the viewer's eyes and the display will vary across the screen. However, if the display were curved in such a manner that the distance between the observer's eyes and the screen's equator were equal anywhere along that equator, then the screen would be kept in focus for the observer. Therefore, there is a need in the art to create such a curved FTIR display screen.
Furthermore, there are various approaches to the problem of efficiently encoding information displayed on a field sequential color display. These algorithms generally presuppose unmodulated uniformity of the base color cycles that are manipulated at the pixel level as performed by U.S. Pat. No. 5,319,491.
FIG. 14 of U.S. Pat. No. 5,319,491 provides a graphic representation of the basic technique for generating color. FIG. 14 of U.S. Pat. No. 5,319,491 provides a timing diagram relating a shuttering sequence of the optical shutter to the 1/180 second strobed light pulses of red, green and blue. It may be appreciated that within any given 1/60 second color cycle various mixes of the three colors may be provided. Thus, as shown in FIG. 14 of U.S. Pat. No. 5,319,491, the first 1/60 second color cycle provides for a color mix 3/16 red, 8/16 blue, and 12/16 green. The mixtures obtainable depend only on the cycle rates of the optical shutter and the color strobing. However, using this method of U.S. Pat. No. 5,319,491 results in a limited palette size. Therefore, there is a need in the art to increase the available color palette.
Furthermore, there are various approaches to the problem of creating voids and complementary standoffs in Microscopic Electro Mechanical Systems (MEMS) structures. Preventing voids in MEMS devices from being filled with the next deposition layer is difficult. One method of attempting to prevent voids in MEMS devices from being filled with the next deposition layer is to deposit sacrificial layers of special material in the void. These sacrificial layers of special material are intended to occupy the void until removed by post-processing steps. Hence the term, “sacrificial,” as applied to these special materials. Subsequent layers have the benefit of a flat, non-void surface upon which to be deposited. Hence, when the sacrificial layer is removed, the geometry of the final system is as intended. A void in this context is an empty volume disposed between solid laminae or their equivalents.
Creating standoff structures in the MEMS industry involves complicated multi-layer work, where all manners of multiple sub-steps and invocation of so-called “sacrificial” layers is required. Creating “valleys” below the level of “plateaus” is a key component in many micromechanical systems. Valleys provide mechanical degrees of freedom in which other elements, which might be ultimately anchored to the plateau, may undergo controlled motion. These “air gaps” are often the key to many MEMS-based devices, but their fabrication remains a complicated process.
MEMS may further require standoffs that are precision registered. In systems such as the Frustrated Total Internal Reflection Display System disclosed in U.S. Pat. No. 5,319,491, this requirement becomes more acute in light of the larger area covered by highly detailed MEMS structures, which become increasingly susceptible to misregistration effects during fabrication. Therefore, a simpler fabrication mechanism is called for, preferably one in which sacrificial layers are essentially self-sacrificing without additional fabrication steps being required to generate the standoffs and interstitial air gaps between them.